/*
 * Copyright (C) 2014 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.j2objc.annotations.WeakOuter;
import java.util.concurrent.Callable;
import java.util.concurrent.Executors;
import java.util.concurrent.RunnableFuture;
import javax.annotation.Nullable;

/**
 * A {@link RunnableFuture} that also implements the {@link ListenableFuture} interface.
 *
 * <p>
 * This should be used in preference to {@link ListenableFutureTask} when possible for performance
 * reasons.
 */
@GwtCompatible
class TrustedListenableFutureTask<V> extends AbstractFuture.TrustedFuture<V> implements RunnableFuture<V> {

    /**
     * Creates a {@code ListenableFutureTask} that will upon running, execute the given
     * {@code Callable}.
     *
     * @param callable the callable task
     */
    static <V> TrustedListenableFutureTask<V> create(Callable<V> callable) {
        return new TrustedListenableFutureTask<V>(callable);
    }

    /**
     * Creates a {@code ListenableFutureTask} that will upon running, execute the given
     * {@code Runnable}, and arrange that {@code get} will return the given result on successful
     * completion.
     *
     * @param runnable the runnable task
     * @param result the result to return on successful completion. If you don't need a particular
     *        result, consider using constructions of the form:
     *        {@code ListenableFuture<?> f = ListenableFutureTask.create(runnable,
     *     null)}
     */
    static <V> TrustedListenableFutureTask<V> create(Runnable runnable, @Nullable V result) {
        return new TrustedListenableFutureTask<V>(Executors.callable(runnable, result));
    }

    /*
     * In certain circumstances, this field might theoretically not be visible to an afterDone()
     * call triggered by cancel(). For details, see the comments on the fields of TimeoutFuture.
     */
    private TrustedFutureInterruptibleTask task;

    TrustedListenableFutureTask(Callable<V> callable) {
        this.task = new TrustedFutureInterruptibleTask(callable);
    }

    @Override
    public void run() {
        TrustedFutureInterruptibleTask localTask = task;
        if (localTask != null) {
            localTask.run();
        }
    }

    @Override
    protected void afterDone() {
        super.afterDone();

        if (wasInterrupted()) {
            TrustedFutureInterruptibleTask localTask = task;
            if (localTask != null) {
                localTask.interruptTask();
            }
        }

        this.task = null;
    }

    @Override
    public String toString() {
        return super.toString() + " (delegate = " + task + ")";
    }

    @WeakOuter
    private final class TrustedFutureInterruptibleTask extends InterruptibleTask {
        private final Callable<V> callable;

        TrustedFutureInterruptibleTask(Callable<V> callable) {
            this.callable = checkNotNull(callable);
        }

        @Override
        void runInterruptibly() {
            // Ensure we haven't been cancelled or already run.
            if (!isDone()) {
                try {
                    set(callable.call());
                } catch (Throwable t) {
                    setException(t);
                }
            }
        }

        @Override
        boolean wasInterrupted() {
            return TrustedListenableFutureTask.this.wasInterrupted();
        }

        @Override
        public String toString() {
            return callable.toString();
        }
    }
}
